Traditional personal hair trimming devices, for example, electric clippers, electric shavers and the like, all are composed of a blade set and a main body assembly. A main body part of the blade set includes a fixed blade and a reciprocating blade which are overlapped with each other. An edge of a front end of the reciprocating blade is provided with a row of cutting teeth. Both left and right edges of each cutting tooth are provided with a cutting edge. An edge of a front end of the fixed blade is provided with a row of comb teeth. An inner surface of each comb tooth contacting the reciprocating blade forms an acute angle with a lateral edge of the comb tooth. The edge of the front end of the reciprocating blade is overlapped with the edge of the front end of the fixed blade. The reciprocating blade is driven by a drive unit stretched out from the main body assembly, so that the edge of the front end of the reciprocating blade makes reciprocating motion with respect to the edge of the front end of the fixed blade, thereby trimming hairs stretching into gaps between the comb teeth of the fixed blade.
However, as the reciprocating blade, particularly the cutting teeth on the edge of the front end of the reciprocating blade, is exposed or partially exposed, a user may be easily hurt, or a psychological fear may be brought to the user.